Etimology
From Middle English techen, from Old English tǣċan (“to show, declare, demonstrate; teach, instruct, train; assign, prescribe, direct; warn; persuade”), from Proto-West Germanic *taikijan, from Proto-Germanic *taikijaną (“to show”), from Proto-Indo-European *deyḱ- (“to show”). Cognate with Scots tech, teich (“to teach”), German zeigen (“to show, point out”), zeihen (“accuse, blame”), Gothic 𐌲𐌰𐍄𐌴𐌹𐌷𐌰𐌽 (gateihan, “to announce, declare, tell, show, display”), Latin dīcō (“speak, say, tell”), Ancient Greek δείκνυμι (deíknumi, “show, point out, explain, teach”), Sanskrit दिशति (diśati, “to point out, show, tell, teach”). More at token.
verb
teach (third-person singular simple present teaches, present participle teaching, simple past and past participle taught)
(ditransitive) To pass on knowledge to.
(intransitive, stative) To pass on knowledge generally, especially as one's profession; to act as a teacher.
(ditransitive) To cause (someone) to learn or understand (something).
(ditransitive) To cause to know the disagreeable consequences of some action.
(obsolete, transitive) To show (someone) the way; to guide, conduct; to point, indicate.
Examples
Can you teach me to sew? Can you teach sewing to me?
Synonyms: educate, instruct
She used to teach at university.
Antonym: learn
The humor of my proposition appealed more strongly to Miss Trevor than I had looked for, and from that time forward she became her old self again; […]. Now she had come to look upon the matter in its true proportions, and her anticipation of a possible chance of teaching him a lesson was a pleasure to behold.
Deep Blue taught us a great deal about the power of the human mind precisely because it could not reproduce the intuitive and logical leaps of Kasparov’s mind. A truly synthetic cell, built from scratch or even from preexisting components, will be a cell without ancestry, and it, too, will teach us a great deal about the underlying complexities of life without actually reproducing them.
I'll teach you to make fun of me!
‘The bliss is there’, mumbled the old man and taught to Heaven.
Blessed God of might most.. teach us the right way unto that bliss that lasteth aye.
Till thy sweet sun uprose, thou keptest all our lay, how we should keep our belief there taught'st thou us the way.
So thus within a whyle as they thus talked the nyghte passed / and the daye shone / and thenne syre launcelot armed hym / and took his hors / and they taught hym to the Abbaye and thyder he rode within the space of two owrys
Etimology
Clipping of teacher.
noun
teach (plural teaches)
(informal, usually as a term of address) teacher