The Second Edition of the 20-volume Oxford English Dictionary, published in 1989, contains full entries for 171,476 words in current use, and 47,156 obsolete words. To this may be added around 9,500 derivative words included as sub-entries.
The Oxford Dictionary says it’s quite probable that English has more words than most comparable world languages. The reason is historical. English was originally a Germanic language, related to Dutch and German. English shares much of its grammar and basic vocabulary with those languages.