ansehnlich
considerable
Of considerable size, quantity, or importance; notable or substantial.
Er hat durch seine Arbeit ein ansehnliches Vermögen angehäuft.
Through his work, he has accumulated a considerable fortune.

considerable / attractive
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considerable
Of considerable size, quantity, or importance; notable or substantial.
Er hat durch seine Arbeit ein ansehnliches Vermögen angehäuft.
Through his work, he has accumulated a considerable fortune.

The word is derived from the verb 'ansehen' (to look at). Something that is 'ansehnlich' (considerable/attractive) is worth looking at—either because it looks good or because it is impressively large or numerous.
Sie hat eine ansehnliche Sammlung alter Bücher.
She has a considerable collection of old books.
The noun that 'ansehnlich' (considerable/attractive) describes reveals the meaning. If it refers to money, a quantity, or size, such as 'Summe' (sum), 'Vermögen' (fortune), or 'Erfolg' (success), it means 'considerable'. If it refers to a person or their appearance, such as 'Mann' (man), 'Frau' (woman), or 'Gestalt' (figure/appearance), it means 'attractive'.
Das Unternehmen erzielte einen ansehnlichen Gewinn.
The company achieved a considerable profit.
In the meaning 'beträchtlich' (considerable), the adjective is often combined with nouns that express a quantity or value. Typical examples are: 'eine ansehnliche Summe' (a considerable sum), 'ein ansehnlicher Betrag' (a considerable amount), or 'ein ansehnliches Vermögen' (a considerable fortune).
Für das alte Auto hat er noch eine ansehnliche Summe bekommen.
He still got a considerable sum for the old car.
beautiful / nice
'schön' and 'ansehnlich' can both describe that a person or thing looks good. 'schön' is the normal and very common word for anything that is visually pleasing. 'ansehnlich' sounds somewhat more elevated or factual and more often means that something makes a good, neat, or attractive impression. For example, you would be more likely to say 'ein schönes Kleid' (a beautiful dress), but 'ein ansehnliches Haus' (an attractive / respectable-looking house) sounds natural if you want to praise the exterior appearance in a somewhat restrained way.

Nach der Renovierung wirkt das alte Haus wieder ansehnlich.
After the renovation, the old house looks attractive again.
Die Lehrerin zeigt der Klasse heute ein schönes Bild aus dem Museum.
The teacher is showing the class a beautiful picture from the museum today.