This highly irregular verb appeared in Definitive Linguistic Notes (DLN) from 1959 as the Sindarin equivalent of Q. auta- “go (away), depart”, itself very irregular, both verbs derived from the invertible root √WĀ/AWA (PE17/148). The Sindarin verb has a present tense form gwaen “I go” and past forms 1st. sg. anwen “*I went” and 3rd. sg. anu/awn “*he/she went”, with these past forms apparently based on an ancient nasal-infixed strong past ✶anwē (from which the archaic Q. strong past †anwe “went” was derived). It has two more forms gwanu/gwawn. These seem to be the equivalent of Q. vanwa “lost” < ✶wanwā.

The present tense form gwaen “I go” is especially peculiar. Compare this to the more regular present tenses cewin “I taste” < kawin(e) (PE22/152) and galon “I grow” < galān(e) (PE17/131). I think the likeliest explanation is that gwaen is derived from an ancient aorist form wa-i-nĭ, with ai becoming ae as was gusual of Sindarin’s phonetic developments. If so, the presents of this verb would be based on √WA and the past inflections based on √AW.

A final twist is that in the note from DLN Tolkien mentions u-intrusion, a sound change parallel to the more common i-intrusion, whereby a final u moved before a preceding consonant. The forms awn and gwawn are thus the u-intruded results of anu and gwanu. This u-intrusion would not occur in forms with further suffixes, like anwen “I went”.

A probably related form gwanwen “departed” appears in the Quendi and Eldar (Q&E) essay from 1959-60 (WJ/378). This could be an independent adjective, but could also be a passive participle of gwae- (or some variant of it), possibly a strengthened or elaborated form of gwanu/gwawn. Note that Q&E also states that:

The only normal derivative [of AWA] is the preposition o, the usual word for ‘from, of’. None of the forms of the element *awa are found as a prefix in S, probably because they became like or the same as the products of *wō, *wo (WJ/366).

Some people believe this indicates that Tolkien rejected other derivatives like gwae-, but since Q&E also contains gwanwen, I think this statement only applies to direct derivatives of AWA, as opposed to gwae- and gwanwen which are derived from the inverted root WĀ.

Neo-Sindarin: How to handle this verb in the context of Neo-Sindarin is unclear. Given the extreme irregularity of this verb, it is tempting to discard it. Unfortunately, we have no other attested Sindarin verbs for “to depart”. Furthermore, common verbs like “go” tend to be irregular in many languages (such as English as “go” vs. “went”), so it makes sense the same would be true of Sindarin. As such, I propose the following conjugation for this verb (hat tip to Gilruin for most of this paradigm; he suggested much better forms than my original ideas):

• Present tense *gwae “go” < primitive ✶gwa-ĭ, with inflections added to this form: gwaen “I go”, *gwael “you go”, etc.
• Past tense awn “went” < ✶anwē with u-intrusion. Inflected forms are based on non-intruded anw-: anwen “I went”, *anwel “you went”, etc.
• Past/passive participle gwanwen “departed”, an elaboration of the older (archaic?) perfective participle gwanu/gwawn.
• Future *gwatha “will go”, *gwathon “I will go”, < ✶wa-thā, wa-thā-nĭ.
• Gerund *gwaed (< ✶wa-itā) and active participle *gwaul (< ✶wa-ālā) “departing”.
• Imperative *gwaw “go!” < ✶wa-ā, as with baw “don’t!” < ✶bā (WJ/371-2).

Finally, this verb means “go” specifically in the sense “depart”, that is: “go away”. For “go (generally and in any direction)”, use the verb men-.

If you dislike this irregularity of gwae- or you believe that Tolkien’s note in Q&E (see above) indicates this verb was rejected along with (most) Sindarin derivatives of AWA, then the neologism haena- “to leave, depart” gives an alternative verb.