To make something warm or heat something up (e.g., food, a room, the body).
冷めたスープを電子レンジで温める。
I heat up the cold soup in the microwave.
手が冷たいときはお湯で手を温めてください。
When your hands are cold, warm them with hot water, please.
部屋を温めてから寝るとぐっすり眠れる。
If you warm the room before sleeping, you can sleep soundly.
To nurture or keep an idea/plan to oneself for a while; to mull over or develop a plan slowly.
新しいビジネス案を半年ほど温めてから発表した。
I developed the new business idea for about half a year before announcing it.
彼は成功のチャンスを狙ってその計画を温めているらしい。
It seems he is keeping the plan to himself, waiting for the chance to succeed.
To renew or rekindle an old relationship or friendship.
同窓会で旧友との関係を温め直した。
At the reunion, I rekindled relationships with old friends.
彼女は昔の恩師との交流を温めている。
She is renewing her contact with a former teacher.
To take something for oneself or appropriate something (context-dependent nuance).
彼はその有利な契約を自分のものに温めてしまったという噂がある。
There are rumors that he appropriated that favorable contract for himself.
情報を外部に出さずに温め続けた結果、彼らが先に利益を得た。
By keeping the information to themselves and holding it, they ended up gaining the advantage first.