The word meticulous was first used in a mid-sixteenth century collection of poetry. It was borrowed from the Latin word meticulosus, which literally meant "frightful" or "timid". This is because of a connection between being attentive to detail and being scared of imperfections - think obsessive compulsive disorder. The root of meticulosus is the fourth declension noun metus, or "fear"; any further beyond that and linguists have no clue. If you know Spanish, metus should be familiar as the root of miedo, and the Latin word was actually used in English with a meaning of "fear" until it died out in the seventeenth century. According to Google NGrams, usage of meticulous in literature over time peaked in the year 1985 and has been declining since, although it seems like Google searches for it have increased since when the website first started measuring it in 2004.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.