mellékajtó означает в английский

side door [side doors]▼◼◼◼noun
[UK: saɪd dɔː(r)] [US: ˈsaɪd ˈdɔːr]

side-door▼◼◼◼noun
[UK: saɪd dɔː(r)] [US: ˈsaɪd ˈdɔːr]

by-door▼noun
[UK: baɪ dɔː(r)] [US: baɪ ˈdɔːr]