I used coconut oil almost every day. I generally put it on before I go to bed as a leave-in moisturizer, but sometimes I will smooth it over frizzy parts during the day. It's great for both of those things, but I don't think it has made a difference for definition.
I use it in my weekly DT. I've used olive oil too, but I think coconut oil has more protein and I like to throw some into my otherwise protein-less hair regimen. My hair always feels soft and moisturized afterward.
I don't know that it would help with curl definition (clumping maybe), but I think it could help with frizz.
CG Since 5/23/09 3a - High Porosity / Coarse Texture on Crown, Medium Texture Beneath CO Wash: Trader Joe's Tea Tree Cond. Condition: Salon Care Honey Almond Cond. Gel: Biotera gel DT: Honey, conditioner, EVOO(1x/wk)
So the coconut oil worked out very well. I put in some leave in conditioner and then scrunched the coconut oil in afterwards. My hair was sooo shiny all day with no frizz and defined curls. however i think I put too much oil in because i had the "wet look" all day. so next time i'm going to put less in.