Some linguists estimate that as much as 80 percent of the lexicon of Old English was lost by the end of the Middle English period, including many compound words, e.g. bōchūs ('bookhouse', 'library'), yet the components 'book' and 'house' were kept.
The Old English synonyms are now mostly either extinct or considered crude or vulgar, such as arse/ass.
Many of these changes came with the introduction of Old Norse and Norman French words, while others fell away due to natural evolution.
Modern English has no Germanic words for 'animal' in the general sense of 'non-human being'.
Old English dēor, gesceaft, gesceap, nēat and iht were all eclipsed by 'animal', 'beast', 'creature' and 'critter'.