Stuff I found when I did a search for "heretick" and "heresy" in SwordSearcher. The commentaries are interesting.Acts 24:13-16 Neither can they prove the things whereof they now accuse me. But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and in the prophets: And have hope toward God, which they themselves also allow, that there shall be a resurrection of the dead, both of the just and unjust. And herein do I exercise myself, to have always a conscience void of offence toward God, and toward men.Strongs:139. hairesis airesiV hairesis hah'-ee-res-is from 138; properly, a choice, i.e. (specially) a party or (abstractly) disunion:--heresy (which is the Greek word itself), sect. 138. haireomai aireomai haireomai hahee-reh'-om-ahee probably akin to 142; to take for oneself, i.e. to prefer:--choose. Some of the forms are borrowed from a cognate hellomai hel'-lom-ahee; which is otherwise obsolete. Titus 3:9-11 But avoid foolish questions, and genealogies, and contentions, and strivings about the law; for they are unprofitable and vain. A man that is an heretick after the first and second admonition reject; Knowing that he that is such is subverted, and sinneth, being condemned of himself.Strongs:141. hairetikos airetikoV hairetikos hahee-ret-ee-kos' from the same as 140; a schismatic:--heretic (the Greek word itself). 140. hairetizo airetizw hairetizo hahee-ret-id'-zo from a derivative of 138; to make a choice:--choose. John Wesley's commentary:Verse 10. An heretic (after a first and second admonition) reject - Avoid, leave to himself. This is the only place, in the whole scripture, where this word heretic occurs; and here it evidently means, a man that obstinately persists in contending about "foolish questions," and thereby occasions strife and animosities, schisms and parties in the church. This, and this alone, is an heretic in the scripture sense; and his punishment likewise is here fixed. Shun, avoid him, leave him to himself. As for the Popish sense, "A man that errs in fundamentals," although it crept, with many other things, early into the church, yet it has no shadow of foundation either in the Old or New Testament. Barne's Commentary:Verse 10. A man that is an heretic. The word heretic is now commonly applied to one who holds some fundamental error of doctrine, "a person who holds and teaches opinions repugnant to the established faith, or that which is made the standard of orthodoxy." Webster. The Greek word here used (airetikoV-- haireticos) occurs nowhere else in the New Testament. The corresponding noun (airesiV-- hairesis) occurs in the following places: Ac 5:17; 15:5; 24:5; 26:5; 28:22, where it is rendered sect; and Ac 24:14; 1Co 11:19; Ga 5:20; 2Pe 2:1, where it is rendered heresy, and heresies. Cmt. on Ac 24:14. The true notion of the word is that of one who is a promoter of a sect or party. The man who makes divisions in a church, instead of aiming to promote unity, is the one who is intended. Such a man may form sects and parties on some points of doctrine on which he differs from others, or on some custom, religious rite, or peculiar practice; he may make some unimportant matter a ground of distinction from his brethren, and may refuse to have fellowship with them, and endeavour to get up a new organization. Such a man, according to the Scripture usage, is a heretic, and not merely one who holds a different doctrine from that which is regarded as orthodoxy. The spirit of the doctrine here is the same as in Ro 16:17, and the same class of persons is referred to. "Mark them which cause divisions and offences contrary to the doctrine which ye have received; and avoid them." Cmt. on Ro 16:17. The word here used is defined by Robinson, (Lex.,) "one who creates dissensions, introduces errors--a factious person." It is not found in classic Greek, but often in ecclesiastical writers. See Suicer's Thesau. Robertson's Word Pictures:Tit 3:10 Heretical (hairetikon). Old adjective from hairesis (haireomai, to choose), a choosing of a party (sect, Ac 5:17) or of teaching (2Pe 2:1). Possibly a schism had been started here in Crete. Refuse (paraitou). Present middle imperative of paraiteô, to ask from, to beg off from. See same form in 1Ti 4:7; 5:11. Possibly an allusion here to Christ's directions in Mt 18:15-17. Dictionaries:Easton Bible Dictionary:Heresy from a Greek word signifying (1) a choice, (2) the opinion chosen, and (3) the sect holding the opinion. In the Acts of the Apostles (Ac 5:17; 15:5; 24:5,14; 26:5) it denotes a sect, without reference to its character. Elsewhere, however, in the New Testament it has a different meaning attached to it. Paul ranks "heresies" with crimes and seditions (Ga 5:20). This word also denotes divisions or schisms in the church (1Co 11:19). In Tit 3:10 a "heretical person" is one who follows his own self-willed "questions," and who is to be avoided. Heresies thus came to signify self-chosen doctrines not emanating from God (2Pe 2:1). I dont know if any of that helps... it is an interesting question, one I have always wondered but never thought to ask. Let's just be sure not to divide into two sects over this issue, else we might be heretics!