1) a word one uses when one does not know the name of someone or something. the word tends to pop into ones mind at the appropriate time. most convenient, yes.
2) a substitute or alternative to using a word that one does now feel comfortable saying
"why, hello, what's your name, Mrs. Thingo?"
"pass me that um...thingo please."
"wow your thingo is so long."
"just a minute. im thingo-ing your grandma."
"what's that thingo called again?"
"shutup or ill kick your thingo."