Saturn in the 10th house synastry means their Saturn falls in your 10th house: where their weight lands in your life. What it feels like from both sides, the gift, the shadow, and how to find your overlays.
Saturn in the 10th house synastry means their Saturn falls in your house of career, reputation and public standing: what you are building and how you are seen doing it. Their judgement lands on your ambitions. This overlay shows up between mentors and students as well as partners, and it tends to make you more accomplished and more accountable at the same time.
Their Saturn in your 10th house
Your work gets a supervisor you did not hire. They ask about the promotion, the side business, the CV, and they have opinions about whether you are living up to your potential. Your career may take off in these years, because the standards are higher and someone is finally watching. Or you may feel you can no longer come home and complain about the job without getting a performance review. Your public image matters to them, sometimes more than your private happiness does. From their side, they feel responsible for your success, and a little exposed by your failures, as if your reputation were partly theirs. They often want for you what they were afraid to want for themselves. Over years, the pushing can become backing, and the pair can look, from the outside, like a formidable team.
The gift
They make you take yourself seriously. The business plan gets written, the raise gets asked for, the sloppy work stops going out under your name. You may end up crediting them for the career you built. Their belief in you is quiet and practical: introductions, edits, a push at the right moment. For them, seeing you succeed on a path they helped shape is one of the deepest satisfactions Saturn offers.
The shadow
The shadow is living your career for their approval. You take the safe job because they respected it, or hide a failure because you cannot face their disappointment. They can treat your public life as a reflection on them and correct it accordingly: what you post, how you dress for events, which friends are good for your image. Being managed is not being supported. If you feel like an employee at home, the arrangement needs renegotiating, not more effort.
Working with it
Decide what success means to you before you ask what it means to them, and write it down so their version cannot quietly replace yours. Invite their advice on specific decisions, then make the call yourself and tell them you have. Celebrate the wins with them, since they helped, and keep a failure or two private if you need to. Ask them about their own ambitions; their Saturn here often hides a career fear they have not voiced.