Dinneen (Foclóir Gaedhilge agus Béarla, 1927):
Tochmharc, a wooing or courtship, wooing, attention; a romance; from to-com-arc.
Tochra, bride-price, marriage-gift, wooing.
Marc, a mark or sign ...; a limit, what is aimed at; a fixed date or time, a turn ...
Marc, a horse.
Margadh, a bargain, esp. a good bargain, a contract or agreement ...; buying or selling, a market.
MacBain (Etymological Dictionary of the Gaelic Language, 1911):
tochmharc, (obsolete) a wooing, so Irish, Old Irish tochmarc: *to-com-arc; see for root iomchorc.
iomchorc, regards, salutation, petition, also Gaelic, Irish iomchomharc, Old Irish imchomarc, interrogatio, salutatio: *imm-com-arc-, from arc, ask,
tochar, tochradh, dowry; cf. Old Irish tochur, placing, from cuire, put. The idea is “something assigned to one.”
eDIL (Electronic Dictionary of the [Medieval] Irish Langauge):
imchomarc. verbal noun of imm-comairc. (a) the act of enquiring about; question, enquiry, interrogation. (b) enquiry (concerning health), greeting, salutation. (c) asking (a request); a petition, boon ...
tochra. verbal noun of do-cren. payment made by bridegroom to bride or bride's father.
do-cren. verb: purchases.
Dinneen:
Cómhárach, a contract.
Im-, iom-, about, around, circum-, amphi-; as intensive, very; in Old Irish it had the effect of a reflexive.
Tochur, putting placing, deliver. See tochar.
Tochar, a journey, meeting or conflict, a crowd.
Tacar, act of collecting, glearning, providing; ... a contrivance, art or pretence
O’Reilly (An Irish-English Dictionary, 1864):
Tochmhaire, a marriage treaty, espousal.
Tochradh, a gift, present reward, portion, dowry, jointure, wealth.
Conclusion:
Tochmharc seems to be a shortened contraction of tochra-cómhárach, a bride-price contract.
