Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
MACCLELLAN
As described in historical dictionaries
Patronymica Britannica (1860)
MACCLELLAN. Gael. Mac-a-ghilledhiolan (pron. Mac-il-iolan.) " TheTson of the Bastard."