I have a lilac bush which this year did not seem to come in as full as the past couple of years. In addition, I see some of the branches have these spiny growths on them. Does anyone know what that is?
Well, that's extraordinary - the growths are typical of galls, usually caused by gall wasps. These are the culprits that cause the gall known as Robin's Pincushion on roses (https://www.wildlifetrusts.org/wildlife-explorer/galls/robins-pincushion), oak apples on oak trees, but I've never seen nor heard of any particular gall wasp that does this on Lilac, nor seen anything like these growths on Lilac either. I might be completely wrong - see what other answers you get, but some information on galls and their causes here https://www.kqed.org/science/23927/what-gall-the-crazy-cribs-of-parasitic-wasps.
If you don't get another more definite answer, if you have a local agricultural extension service (I think that's what they're called, I'm in the UK so these services are only something I've heard mentioned on here), ask them. I'd be fascinated to hear what they say...
Joe, this is not a Lilac, grins. I am pretty sure this is a Witch Hazel: Hamamelis virginiana. Wonderful large shrub small tree!!
It is common to have different shrubs/trees grow in the same spot. I think this is a wimpy witch hazel integrated with the lilac shrub.
Very interesting, dying to see how this turns out! Thanks, Joe!
Do the leaves look familiar?