Lack of money prevented us from taking a holiday this year.
Explanation: "Lack" means the absence or shortage of something, which fits the context of not having enough money.

This blue-flower is known by various names in other parts of England.
Explanation: "Various" means different or diverse, which fits the idea of the flower having multiple names.

Why can't you do this favor for me? I've helped you often.
Explanation: "Favor" refers to a kind or helpful action, which matches the context of asking someone for a help.

When there was a short pause in the conversation, I asked if anyone would like anything to drink.
Explanation: "Pause" refers to a temporary stop or break in activity, which fits the context of a break in conversation.