The most common and most likely answer to this crossword clue is the 8 letter word TOPOLOGY
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More clues leading to the result TOPOLOGY
Buddy explains!

The straight part
We know that "branch of maths" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case branch of maths = topology.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 TOPOLOGY mean?
TOPOLOGY noun- A branch of mathematics studying those properties of a geometric figure or solid that are not changed by stretching, bending and similar homeomorphisms.
- A collection τ of subsets of a set X such that the empty set and X are both members of τ, and τ is closed under finitary intersections and arbitrary unions.
- The anatomical structure of part of the body.
- The arrangement of nodes in a communications network.
- The properties of a particular technological embodiment that are not affected by differences in the physical layout or form of its application.
- (topography) The topographical study of geographic locations or given places in relation to their history.
- The art of, or method for, assisting the memory by associating the thing or subject to be remembered with some place.