Faol or Faolchú are words for wolf. The personal name Faolán (thus Ó Faoláin eg. Whelan/Phelan etc.) is a dimunitive form. The old Irish form of the word is Fáel.

DIL has the following which is relevant:

2 fáelad
Keywords: become; behave; wolf

(vn.) to become or behave like a wolf (?): Laighnech Faeladh .i. fer eissidhe no theghedh fri faeladh .i. i conr[e]achtaibh .i. a r[e]achtaibh na mac tire téghedh `used to shift into wolf-shapes ‘ Cóir Anm. 215 . Cf. in tan badar oc f.¤ i crich Connacht occa munud BDD 20 . Cf. 1 fáelad, and faílid.

m. (= fáel + fer ?) fial in f.¤ `noble wolf-man’ Arch. Hib. ii 49.6 ( LL 181 b 47 ).

io,m. (2 fáel?) wolfhunter (?): mac do Laegaire Lingid | f.¤ is cimid gan ceas, Ériu x 81 § 52 . Lingit mac Loegaire iar ló | ba f.¤ frithirgó LL 165 b 37 .

Cú Allaidh/Madra Allaidh are other terms for a Wolf, both show up in Dinneen, “Cú Allaidh” is mentioned in eDIL entry for Fáelchú.