WordNet records no synonym and no antonym for follow-through. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
carrying some project or intention to full completion
“I appreciated his follow-through on his promise”
the act of carrying a stroke to its natural completion
“his follow-through was straight down the line toward the target”
Synonyms, antonyms and the broader and narrower relations for follow-through come from Princeton University’s WordNet. Full sources and licences.