The most common and most likely answer to this crossword clue is the 5 letter word TREAT
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More clues leading to the result TREAT
Buddy explains!

The straight part
We know that "Negotiate terms" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case negotiate terms = treat.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TREAT mean?
TREAT noun- An entertainment, outing, food, drink, or other indulgence provided by someone for the enjoyment of others.
- An unexpected gift, event etc., which provides great pleasure.
- A snack food item designed to be given to pets.
- A parley or discussion of terms; a negotiation.
- An entreaty.
- To negotiate, discuss terms, bargain (for or with).
- To discourse; to handle a subject in writing or speaking; to conduct a discussion.
- To discourse on; to represent or deal with in a particular way, in writing or speaking.
- To entreat or beseech (someone).
- To handle, deal with or behave towards in a specific way.
- To entertain with food or drink, especially at one's own expense; to show hospitality to; to pay for as celebration or reward.
- To commit the offence of providing food, drink, entertainment or provision to corruptly influence a voter.
- To care for medicinally or surgically; to apply medical care to.
- To subject to a chemical or other action; to act upon with a specific scientific result in mind.
- To provide something special and pleasant.