HAIRSPLITTER
hairsplitter
(noun) a disputant who makes unreasonably fine distinctions
Source: WordNet® 3.1
Etymology
Noun
hairsplitter (plural hairsplitters)
A stickler person who makes extremely, possibly excessively, fine distinctions (who would separate something as fine as a hair into two pieces and distinguish them).
Source: Wiktionary
Hair"split`ter, n.
Definition: One who makes excessively nice or needless distinctions in
reasoning; one who quibbles. "The caviling hairsplitter." De Quincey.
Source: Webster’s Unabridged Dictionary 1913 Edition