Appreciative = feeling or showing gratitude, pleasure ; understanding.

• The opening lecture of his course was listened to by a large and appreciative audience.
• He was an earnest and appreciative student.
• I am appreciative of your efforts to improve the lots of orphans.
• He smiled appreciatively at her.
• Her novel received a number of appreciative reviews.
• I am appreciative of the support and help given by you in my extremities.

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Appreciable = considerable, substantial, large or important enough to be noticed.

• Pupils may have to travel appreciable distances.
• An appreciable amount of liquor is being consumed in Kerala , which is not a healthy trend.
• He perceived an appreciable difference in the enthusiasm of students after the new principal took charge.
• After using chemical manures , there was an appreciable improvement in the agricultural productivity.