Chelsea is not a nickname, it is a Cantonese transliteration. For example, Arsenal's Cantonese transliteration is Arsenal, Everton's Cantonese transliteration is Everton, etc. In fact, English clubs basically have nicknames or nicknames. Take this season's top 20 as an example:
Manchester United: Red Devils. Liverpool: Red Army. Huddersfield: Territory. Manchester City: Citizen, Sky Blue. West Brom: Knickerbockers, Thrushes. Chelsea: Blues, veterans. Watford: Hornets. Southampton: Saints. Tottenham: Tottenham. (We usually call this team Tottenham Hotspur. In fact, Tottenham is the nickname) Burnley: Purple Legion. Stoke City: Potters, City in the Sky. Everton: Toffees. Swansea: Swansea. Newcastle United: Magpies. Leicester City: Foxes. Arsenal: Arsenal, Gunners. Brighton: Seagull. Bournemouth:Cherry. Crystal Palace: Eagles. West Ham United: Blacksmith, Hammer
Some other English clubs that are not in the top league this season, but are also famous, such as Charlton: Braves, Sharks. Fulham: Farmer, farmer. Aston Villa: Villa man. Sunderland: Black Cats. Norwich: Canaries. Derby County: Rams. Leeds United: Young Guards, White Legion.