Cuireadh -mā le cinn eile ach is le cuidiú na hiarmhíre f. *-tu- a bunaíodh ainm briathartha ar thamhan lagbhriathair de ghnáth: m.sh., L2a moídem ‘maíomh’ (gin. moíd†me) < *moið-i-ṽa < *moidīmā (6.2a; t. l. -moídi), L1 marbad ‘marú’, léiciud ‘ligean’ (gin. marb†th-o/-a, léic†th-eo/-ea; 18.2) < *marw-a-θuh, *lēg-i-θuh < *-ā-tus, *-ī-tus (6.4). D’úsáid cúpla tréanbhriathar *-tu- freisin ach bhí *-mu níba choitianta, go háirithe i gcás S2; m.sh. mess ‘meas’ (gin. mess-o/-a) < *med-tus- (6.2; t. l. -midethar), gním ‘gníomh’, dénum ‘déanamh’ (gin. gním-o/-a, dén†m-o/-a) < *gnī-mu-s, *de-gnī-mu-s (*gnī- < *ĝneh₁-?). (…)

[The ending -mā was added to other ones but it’s with the help of masc. ending *-tu- that typically verbal nouns were formed from weak verb stems: e.g., W2a moídem ‘boasting, declaring’ (gen. moíd†me) < *moið-i-ṽa < *moidīmā (6.2a; pres. indic. -moídi), W1 marbad ‘killing’, léiciud ‘letting, allowing’ (gen. marb†th-o/-a, léic†th-eo/-ea; 18.2) < *marw-a-θuh, *lēg-i-θuh < *-ā-tus, *-ī-tus (6.4). A few strong verbs used *-tu- too but *-mu was more common, especially in the case of S2; e.g. mess ‘judging, estimating, opining’ (gen. mess-o/-a) < *med-tus- (6.2; pres.indic. -midethar), gním ‘acting, doing’, dénum ‘doing’ (gen. gním-o/-a, dén†m-o/-a) < *gnī-mu-s, *de-gnī-mu-s (*gnī- < *ĝneh₁-?). (…)]