1. with a purpose or plan
deliberate act/plan/ruse, act deliberately
The word 'deliberate' can be used as an adjective to describe doing something intentionally with purpose: "I deliberately put the cake over there so I wouldn't eat it all!" "This tactic is a deliberate ploy to encourage us to give up more of our shares." You can use this word in social or professional contexts.
2. discuss or talk about things (carefully/seriously)
deliberate on/over the decision/matter, after much deliberation
Deliberate can also be used as a verb to describe the process of considering or deciding something: "The judges will now take a few moments to deliberate on a decision." "I have been deliberating on moving house for a long time now. It's time I came to a decision." This use of 'deliberate' is mostly used in professional situations, either in relation to meetings and team discussion; or in a courtroom setting.