Princely is especially used of treasure, expenditure, gifts, etc., as princely munificence, a princely fortune, where regal could not so well be used and royal would change the sense.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

noble The country was governed by a French noble family.
imperial In the Middle Ages, Aalen was a free imperial city.
sovereign Queen Victoria was the sovereign of Great Britain.
sumptuous The sumptuous residence of a government official was pillaged.
aristocratic His dress somehow gives an aristocratic impression.

Popularity over time

Word	1850 → 2019	Trend
princely		steady
noble		falling
imperial		rising
sovereign		steady
sumptuous		rising
aristocratic		rising

Use in printed books, per decade from 1850 to 2019.

By length

5 letters: large¹, grand¹, royal², noble², regal²
6 letters: august², deluxe², gilded², princy
7 letters: liberal³, stately², exalted³, opulent³, regally³
8 letters: imperial⁴, generous³, majestic³
9 letters: sovereign², luxurious⁴, dignified³, sumptuous², bounteous
10 letters: munificent, princelike, princelily
11 letters: magnificent⁴
12 letters: aristocratic⁵

The small number after each word is its number of syllables (royal² = 2 syllables).

In other languages

Français: princier
Italiano: principesco
Deutsch: fürstlich