painstaking
adj.describing work that is done with great care and attention to detail. It usually takes a lot of time and effort to finish.
adj.characterised by extreme care, precision, and thoroughness in execution. Often implies a laborious process that requires significant mental or physical effort.
“The artist spent painstaking hours painting the small details.”
“The researchers conducted a painstaking analysis of the data to ensure no small error went unnoticed.”
“The restoration of the ancient manuscript required painstaking attention to the delicate ink, as any sudden movement could cause the fragile pages to tear.”
“It is worth noting that his foray into costly online clinics bears no resemblance to the immensely painstaking procedures behind an ADHD diagnostic procedure as laid out by Nice guidelines .”
“The purpose was to spare the human researchers the tedious and painstaking work of hand-classifying every project in the data set.”
From pains + taking; see take pains. The /ˈpeɪnˌsteɪkɪŋ/ pronunciation which dominates in the United States suggests a reanalysis of the word as pain + staking.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.