Thanks for the note.Let me answer your question in parts:
 There appear to be three distinct (read here: unrelated)"strains" that gave rise to Lenaghan families from Ireland - a. those families that originated from a sept in Tipperary (These families usually now spell the name Lenihan); b. those families that originated from a sept in Roscommon; and c. those families that are actually Scots-Irish McClenaghans that over time dropped the Mc-. (These families are to be found in Ulster.) Furthermore, the meaning of the name differs depending on its origin.For example, the name of the Roscommon sept is said to be derived from the Irish word "sorrowful."The Scots-Irish name is said to mean "Son of the servant of Saint Onchu." [How's that for difference!]
 I'm sorry to disappoint you but there is no family crest.Coats of arms are granted to individuals not families and are therefore personal property.Further, the Lenaghan coats sometimes found in genealogical books were actually only granted -- to two members of the southern Lenihan family -- in the 19th century!They can only be legitmately used by their descendants.
 I'm also interested in your Patrick Lenaghan. One of my distant cousin, Patrick Lenaghan, migrated to England by the 1840's.He was a barrister of Middle Temple.Does this sound familiar?
Anyway, if I can be of any further service drop me a note.