Many Irish resources for the basic name, the earliest documented version seeming to be Olanan in 1182 AD, on rootsweb site pointed to by
www.klennan.com .
A suggestion: don't get hung up on the specific spelling, since many Irish ancestors, up to 1900s, just affixed their 'X' marks. Maybe you might even need to consider 'Ly' versions, Glenn*n or MacLennan!
From painful experience of initially concentrating on Lennan, and missing many ancestors.
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