Why is aniline less basic than ethylamine ?

Explanation

Aniline may be regarded as a resonance hybrid of the following five contributing structure (I-V)
Due to resonance, the lone pair of electron on the nitrogen atom gets delocalised over the benzene ring and thus it is less easily available for protonation. At the same time nitrogen acquires some positive charge (II to IV) and this repel the incoming proton.