1To stop up or close an opening — to block, plug a hole or gap, or cover (one's eyes, ears, etc.).
パイプの穴を布でしっかり塞いだ。
I firmly plugged the hole in the pipe with cloth.
うるさくて、両手で耳を塞いだ。
It was so loud that I covered my ears with both hands.
隙間から風が入ってくるので、テープで塞いだ。
Wind was coming in through the gap, so I sealed it with tape.
2To stand in the way of or obstruct — to block a road, passage, or opportunity.
工事のトラックが歩道を塞いでいる。
A construction truck is blocking the sidewalk.
大きな荷物が玄関を塞いでいて出られない。
A large package is blocking the entrance, so I can't get out.
彼の反対意見が議論の進行を塞いでしまった。
His objection ended up obstructing the progress of the discussion.
3To occupy or fill up — to take up a seat, space, or block of time.
会議室は午後は予約で塞がっている。
The conference room is fully booked in the afternoon.
彼はいつも隣の席を荷物で塞いでいる。
He's always taking up the seat next to him with his bags.
休日は予定が次々に塞がってしまった。
My plans for the holiday filled up one after another.
4To fill or perform a role or duty (a formal, somewhat literary usage). Rarely used in modern spoken Japanese.
村の行事では、代々長老の家柄がその役を塞いできた。
At the village's events, the elder's family has for generations filled that role.
5To feel depressed, gloomy, or in low spirits — used intransitively for one's mood or state of mind.
最近ずっと塞いでいるようで、話しかけても返事がない。
They've seemed down lately and don't respond even when spoken to.
失恋してから、彼女は気が塞ぎがちになった。
Since the breakup, she's tended to feel down.