ditto, my child didn't really speak until three, and it worried me at the time - although her comprehension, humour and communication in every other way was great (she would act out what she wanted, people KNEW what she wanted, even without words). Everything Marydean says, i second.

it was so weird, after three years of just "mum mum", "dad dad" and "mummy booby" (for milk), she turned three, and it was like a waterfall was turned on! all of sudden, complete sentences, from nowhere.

i remember her 18 month health check, when SUPPOSEDLY, babies are meant to have ten words by then (and my child sure did not). They all learn at their own pace.
I agree with this! You are looking for communication, not so much language at this stage. Those social skills of enjoying shared games such as peek-a-boo and joint attention such as looking at you and back at something exciting like a truck and back to you are much more important.

If it helps, my son had over 100 words at his 18 month check up and is autistic and has severe language delays. He had friends from mother's group who could barely scrape the 10 words together at that point but went on to develop completely typical language skills.