If someone is companionable, they are friendly and pleasant to be with — easy company, not sharp, good to spend a long afternoon with. It describes a manner, not a job. A companionable silence is a quiet that still feels kind, the sort you do not need to fill. The word is a little literary; in everyday talk people more often say friendly or easy to be with. You can use it of a person, and sometimes of a mood or an evening that feels like good company.