>Thank you, Yonah.
>I'm of course aware of the orthodox etymology. It doesn't make much sense;
>why the tav-form? Presumably, tav-nouns are frozen 2ms future tense verbs,
>the least likely form for "to teach."
It makes lots of sense, and is part of a very widespread and
well-understood pattern. TAF, along with MEM, is used as a prefix to
create a noun; frequently, a final HEH accompanies these nouns.
TODAH (a noun from Y.D.H)
TORAH (a noun from Y.R.H)
TXINA (a noun from X.N.N)
T'ENA ("fig")
T'HILA ("praise")
TUGA ("grief")
T'ALA ("aqueduct")
T'FILA ("prayer")
TIKVA ("hope")
etc.
When the root ends in HEH, a second HEH canno be added. When the root
begins with VAV, rather than "ti-" the word obviously starts "to-."